1. Field of the Invention
The present invention relates to creation of a table used for separating a given color into colors of the coloring agents available in a particular image formation apparatus.
2. Related Background Art
Conventionally, processing for separating a color into data corresponding to the coloring agents available in a color printer (hereinafter, called “ink color separation processing”) is as shown in FIG. 22. Hereinafter, an explanation of the ink color separation processing will be given with reference to FIG. 22.
Numeral 2201 denotes a luminance/density conversion unit, numeral 2202 denotes a UCR/BG processing unit, numeral 2203 denotes a BG quantity setting unit and numeral 2204 denotes a UCR (under-color removal) quantity setting unit. In the luminance/density conversion unit 2201, luminance information of 8-bit data of R′, G′ and B′ that are being input is converted into C, M and Y data based on the following expressions:C=−α log(R′/255)  (1)M=−α log(G′/255)  (2)Y=−α log(B′/255)  (3)where α denotes an arbitrary real number.
Next, the C, M and Y data are respectively converted by use of β(Min(C, M, Y),μ) set in a BG coefficient setting unit 1603 and a value μ% set in a UCR coefficient setting unit 1604 as follows:C′=C−(μ/100)×Min(C,M,Y)  (4)M′=M−(μ/100)×Min(C,M,Y)  (5)Y′=Y−(μ/100)×Min(C,M,Y)  (6)K′=β(Min(C,M,Y),μ)×(μ/100)×Min(C,M,Y)  (7)where the β(Min(C, M, Y), μ) denotes a real number which is varied by the Min(C, M, Y) and the value μ. A dyeing method of K ink can be set according to a value of this real number.
Since the UCR quantity and the BG quantity have a great influence on a color reproduction region of the color printer and on the degree of graininess that appears in printing performed by the printer accompanied by the dyeing method of K ink, those quantities become important parameters for the color printer.
However, conventionally, since the UCR quantity is calculated by multiplying a UCR coefficient μ by the Min(C, M, Y), and the BG quantity is calculated by multiplying the BG coefficient β by the UCR coefficient μ by the Min(C, M, Y), it was impossible to set optimized UCR and BG quantities for every hue, and as a result the following problems existed.
For a certain hue of a target printer, even though that color of higher chroma can be outputted, the ink color separation processing which would be needed to produce that color cannot be provided.
Again, even though the effect of graininess caused by the K ink can be reduced more based on appropriate combination of ink quantities, the corresponding ink color separation processing cannot be provided.
In the above conventional example, the non-linear characteristics that obtain in a case of the mixture of plural inks cannot be sufficiently compensated for or taken into account, and distorted characteristics remain in lightness, hue and chroma.